1. Field of the Invention
The present invention relates generally to wheeled load carriers towed behind an individual, and more particularly to a stable monowheel travois with a counterweight feature.
2. Discussion of the Related Art
History presents a diverse array of devices which may be used to tow or pull a load behind an individual. The purpose of these devices is to assist an individual in transporting the load, especially those loads weighing more than an individual may comfortably carry for any significant distance. These apparatus generally have some type of frame for supporting the load, or cargo and one or more wheels. Of particular interest herein is a device commonly referred to as a travois, which is towed behind an operator and has a load carrying frame with a single wheel.
The single wheeled, or monowheel travois is most efficient because it is generally smaller and lighter than multi-wheeled carriers allowing it to navigate narrow trails and turn very quickly and easily. However, several problems exist with monowheel travois designs, including lack of stability, an adequate stand-alone capability, and leg or foot contact by the operator when pulling the travois.
The critical problem of a monowheel configuration is the inherent instability of a single wheel. The load carried on the travois has a center of gravity, which is the point though which the earth's gravitational force is exerted. The gravitational force is counteracted though the tire contact patch, which is the point of contact between the wheel, or tire and the ground. When the center of gravity of the cargo is not aligned with the contact patch it forces the travois to tilt, or lose balance. Also, the higher the center of gravity is above the contact patch, the greater force it will exert when it is not aligned, because the span between the center of gravity and the contact patch behaves like a lever to assist the center of gravity in tilting the travois. The lever, or span is known as a torque arm, and the tilting force is known as a torque, or torque force. The longer the torque arm, the greater the torque force.
There are two important travois torque arms. First, the tilting torque arm, discussed above, is a side-to-side, or transverse torque arm that causes the travois to tip from side-to-side. The transverse torque arm produces a torque force when the center of gravity of the cargo is positioned to the left or the right of the tire contact patch, as seen from the perspective of the operator pulling the travois. The second torque arm is a front-to-rear or longitudinal torque arm. It produces a torque force when the center of gravity of the cargo is forward-of or behind the tire contact patch, as seen from the perspective of the operator pulling the travois. This results in a longitudinal torque force that pushes the front of the travois down towards the ground resulting in what the operator feels as a weight that must be supported while pulling the travois. The length of both torque arms is the distance from the cargo's center of gravity to the contact patch.
Rather than addressing the direct cause of the monowheel travois instability problem, i.e., the length of the torque arms, and the resulting increased torque forces, existing devices simply use the operator to counter the torques generated by the load's center of gravity. This method does not decrease the size, or magnitude of the travois torques, but rather forces the operator to constantly counteract the large torque forces. Ceaselessly balancing, and supporting the travois soon tires and irritates the operator which explains why these devices are not in common use today in spite of their numerous advantages over larger and heavier multi-wheeled carriers. Accordingly, there is still a need for a monowheel travois that is stable and easy to operate.